Autonomic orienting response (OR) nonresponsiveness is a widely replicated and temporally stable finding in schizophrenia research. Recent evidence that OR nonresponsiveness does not occur more frequently in depression than in normal samples suggests that this abnormality may be a specific to schizophrenia. To evaluate further the specificity of OR nonresponsiveness in 40 schizophrenic and 24 bipolar manic patients, and 20 control subjects. Both the skin conductance and finger pulse volume OR (SCOR and FPV-OR) will be evaluated simultaneously with OR nonresponsiveness defined as the absence of both SCOR and FPV-OR to the first three of 15 innocuous tones. This two-component criterion for OR nonresponsiveness recently was found to differentiate depressed from schizophrenic patients. To discriminate further between schizophrenia and mania, subjects will undergo an attentional task where they will be asked to respond behaviorally to tones of a certain pitch. Electrodermal and FPV responsitivity to task relevant and irrelevant tones will be assessed. Autonomic responsitivity in depressed and schizophrenic patients have shown important differences using this paradigm in previous investigations. All measurements will be bilateral to permit the evaluation of specific asymmetry patterns in the manic subjects. In order to evaluate temporal stability, both OR responsitivity and autonomic responsitivity to the attentional task will be assessed on two occasions separated by four weeks in a manner designed to reduce practice effects.